Hospital patients hoping to recover quietly from their operation are in for a shock. Today's hospitals are noisier than ever, and the problem is getting worse.

A team at Johns Hopkins University in Baltimore, Maryland, says that average noise levels at the Johns Hopkins Hospital (JHH), the top-ranked hospital in the United States for the past 14 years, exceed the threshold recommended by the World Health Organization (WHO).

If it's that bad at JHH, they say in the Journal of the Acoustical Society of America1, it is probably at least as bad in other hospitals throughout the developed world.

Many of the units they studied do not get significantly quieter at night-time. "We were surprised that it was absolutely impossible to distinguish night from day," says team leader Ilene Busch-Vichniac. Nor does it make much difference where you are. Even the newest patient-care building in the hospital, supposedly designed for quieter acoustics, was no less noisy than the older parts of the hospital.

"People have been complaining about hospital noise for years, but little has been done about the problem," says Busch-Vishniac's colleague, acoustic engineer James West. It seems the complaints have actually been going on for centuries. Florence Nightingale wrote in 1859: "Unnecessary noise is the most cruel absence of care which can be inflicted either on sick or well."

It isn't just a matter of disturbing the patients' peace, the researchers say. Noise contributes to stress in hospital staff, and some studies have suggested that their memory and other mental functions can be impaired by it. And high sound levels have been found to slow down wound healing2. "Noise makes it difficult for patients to get well," says Busch-Vishniac.

What was that?!

“Unnecessary noise is the most cruel absence of care which can be inflicted on the sick.”

Florence Nightingale

Busch-Vishniac and her colleagues re-analysed old data and found that not one of more than 20 hospitals investigated worldwide since the 1960s complied with the WHO guidelines, which stipulate that noise be kept below an average of 35 decibels (dB) during the day and 30 dB at night. This is about equivalent to a loud whisper.

Instead, noise levels have been gradually rising, from around 40 dB in the early 1960s to about 60 dB today, about the level of a person talking loudly.

The team decided to see how the renowned JHH fared by measuring sound levels at five different locations within the hospital. All the averages were about 20 dB above the WHO guidelines, with the maximum level at around 70 dB, equivalent to the noise on a busy street. "I don't believe that bringing down noise to WHO levels is feasible at present," Busch-Vishniac says.

You'll have to speak up!

The researchers say that hospital staff may need to raise their voice routinely to be heard, potentially leading to misunderstandings. If noise levels continue to rise at the same rate, they write, "it might eventually be difficult to communicate orally, even by means of shouting."

Hospitals are noisy in part because they don't have many of the soft fabrics that absorb noise in domestic settings, since these can harbour infections. The researchers say that air-conditioning units contribute to low-frequency sound, and they think that the increasing number of beeping alarms on medical equipment might be responsible for much of the higher frequencies. "Those are very irritating," Busch-Vishniac admits. And previous research3 shows that the beeps are mostly ignored by staff anyway, she says.

The 24-hour intensive-care units can be particularly noisy, and this has been suggested as a possible cause of psychotic episodes experienced by some patients.

The Johns Hopkins engineers are now helping to devise sound-absorbing panels for hospitals. They managed to quieten the intensive-care unit of one oncology department, where infections are particularly risky, by fixing such panels to the ceiling with Velcro. But West warns that "the majority of hospital noise problems are not that easy to fix".